In higher plants under low
oxygen or hypoxic conditions, the
phytohormone ethylene and
hydrogen peroxide (H2O2) are involved in complex regulatory mechanisms in
hypoxia signaling pathways. The
respiratory burst oxidase homolog D (RbohD), an
NADPH oxidase, is involved in the primary stages of
hypoxia signaling, modulating the expression of downstream
hypoxia-inducible genes under hypoxic stress. In this study, our data revealed that under normoxic conditions, seed germination was delayed in the rbohD/ein2-5 double mutant, whereas postgermination stage root growth was promoted. Under submergence, the rbohD/ein2-5 double mutant line had an inhibited root growth phenotype. Furthermore,
chlorophyll content and leaf survival were reduced in the rbohD/ein2-5 double mutant compared with wild-type plants under submerged conditions. In quantitative RT-PCR analysis, the induction of
Ethylene-responsive factor 73/
hypoxia responsive 1 (AtERF73/HRE1) and
alcohol dehydrogenase 1 (AtADH1) transcripts was lower in the rbohD/ein2-5 double mutant during hypoxic stress than in wild-type plants and in rbohD and ein2-5 mutant lines. Taken together, our results indicate that an interplay of
ethylene and RbohD is involved in regulating seed germination and post-germination stages under normoxic conditions. Moreover,
ethylene and RbohD are involved in modulating seedling root growth, leaf
chlorophyll content, and
hypoxia-inducible gene expression under hypoxic conditions.